Recovery of chlorine



Feb- 8' 1927 A. GUYER ET AI- RECOVERY OF CHLORIHE Filed April 19. 1926 n, 'l U f ATTORNEY,

Illllvl INVENTOR Jesse Aua MAumcE CTAYLOR *III SESSO Wx Patented Feb. '8, 1927.

UNITED STATES PAT-ENT OFFICE.

JESSE GUYER, OF LA SALLE, AND MAURICE C. TAYLOR, OF NIAGARA FALLS, NEW YORK, ASSIGNOBS T0 THE HATHIESON ALKALI WORKS, INC., OF NEW YORK, N. Y.,

A GOBPORATION Ol' VIRGINIA.

RECOVERY Ol' CHLORINE.

application mea apra is, 192s. semi semanal.

This invention relates to improvements in the separation and recovery of chlorine from gas mixtures such as the residual ases, or so-called blow-off gases, produce in the manufacture of liquid chlorine by compression and liquefaction methods. In the manufacture of liquid chlorine, chlorine gas produced for example by the electrolysis o alkali chloride brnes, is commonl dried, for example with sulphuric acid, t en mechanically compressed, and then cooled with liquefaction of the greater part of the chlorine and separation of the residual or blowoff gases. larly to improvements in the utilization ofsilica gel for the separation and recovery of chlorine from such gas mixtures.

These residual gases are composed principally of air, hydrogen and chlorine, the chlorine commonly being present in amounts approximating.50% by volume. The chlorine content of such gas mixtures is com-' monly recovered by using the gases-to chlo rinate alkaline liquors such as solutions or suiensions of sodium hydroxide or calcium hy roxide, or to chlorinate limefor the production of bleaching powder, but for the purposes of manufacturing liquid chlorine it is desirable to recover this chlorine directly when it can be so recovered economically.

The chlorine content of such gas mixtures can be separated by adsorption on various solid absorbent mediums, but several difficulties are involved in the practical utilization of such methods, and they have not heretofore corne into commercial use in liquid chlorine plants. To refer to two solid absorbents that have been suggested, namely, activated'carbon and silica gel, -highly activated carbon catalyzes the reaction between chlorine and hydrogen resulting in the formation of hydrochloric acid which is 0bjectionable, while less active carbon has an absorptive capacity so low as to require the use of excessive amounts of the absorbent, and- .the thermal conductivity of silica gel is so low that with gas mixtures containing such a high proportion of the component to be adsorbed the ratio between the period when .the gel is capable of usefully adsorbing chlorine and the period necessary to separate the adsorbed chlorine from the gel and bring the This invention relates particu- ,P

gel back toits original condition with usual methods is` inordinately small. From the practical standpoint, this disadvantage is particularly marked where it is necessary to andle fairly large amounts of the gas mixture.

Under certain conditions, however, chlorine can be separated from such gas mixtures by adsorption on silica gel and recovered directly from the silica gel and this.

invention provides a special method of using silica gel 1n the separation and recovery of chlorine from such makes it possible to e ect the recovery economically and eliiciently in a manner adapt` ed to practical purposes, even where the gas mixture contains a large proportion of chlorine and Where it is necessary to handle large amounts of the gas mixture. The present inventiony relates particularly to improvements in the utilization of silica gel for the separation and recovery of chlorine from gas mixtures containing chlorine.

The complete process comprises production of chlorine as, for example by electrolytic methods; rying'of the chlorine gas; compression of the chlorine gas in mechanical compressors; cooling of the compressed gas and liquefaction of the greater part of the chlorine; separation of the residual gas; removal of chlorine from the residual gas by adsorption on silica gel; separation of adsorbed chlorine from the silica gel; and liquefaction. of the concentrated chlorine so obtained, for example by cyclically returning it to the mechanical compressors. This invention relates particularly to improvements in the steps of adsorption of the chlorine on silica gel and the separation of adsorbed chlorine from the silica gel.

According to the present invention, the gas mixture containing chlorine is subjected to treatment with silica gel under a pressure advantageously superatmosp'heric and the adsorbed chlorine is separated from the silica gel under a lower pressure while the temperature is maintained low enough to provide a useful margin in content of chlorine adsorbed on the silica gel over the pressure dilerential used. The pressure maintained during separation of the adsorbed chlorine from the silica gel may advantageously be much lower than atmospheric pressure. The

as mixtures which n the remainder of the temperature maintained durin the operation may advantageously be muc lower than ordinary atmospheric temperatures, refrigeration being employed with advantage The cycle of the special process of the 1nvention com rises adsorption of chlorine on the silica ge during which periodthe temperature of the silica gel tends to rise due to the heat of adsorption, followed b separation of adsorbed chlorine by a re uction of pressure during which period the temperature of the silica gel tends to drop due to the heat absorbed in vaporization of the chlorine.

The adsorptive capacity of silica gel for chlorine decreases with increasing temperature and the heat of adsorption of chlorine on silica gel is substantial. In the usual agplications of silica gel, the component'of t gas mixture to be adsorbed 1s present in but small amount so that the balance of the gas mixture is available to absorb in'substantial measure Y the heat of adsorption. llfith gas mixtures containin a high roportion of chlorine, such as t ose to w 'ch this invention particularly relates, however,

as mixture is necessarily much less ei'ective in absorbin the heat of adsorption while the chlorine as a comparatively high heat of adsorption. Due to its low thermal conductivity, moreover, silica gel cannot be eiliciently cooled by any ordinary external cooling means. As a result the adsorptive capacity of the silica gel is limited by the temperature rise due to the heat of adsorption as well as by the actual quantit of chlorine adsorbed. In carrying out t is invention, the heat of adsorption is removed from the silica l, in larve part, by the vaporization of e adsorbed chlorine which is carried out under reduced pressure, under which conditions the low thermal conductivity of the silica gel becomes unimportant, and diiliculties that miglit'be due to the temperature rise during t e adsorption period are avoided by making the cycle of operations short. When artificial cooling or refrigeration is employed in carrying out the invention, it is advantageously used to reduce the temperature range over which the entire cycle of operations 1s carried out rather than to maintain an additional temperature diierential sorbed chlorine from the silica gel is effected primarily by pressure reduction, promoting high ca acity per pound of silica gel er hour wit respect to chlorine.

T e invention will be further described, and in more detail, in connection with specific operations in accordance with the invention, and in this further description reference `will be inade to the accompanying drawings which illustrate in a diagrammatic and conventional manner apparatus adapted for carryinvr out the process of the invention. In t ie accompanying drawings, the absorbers are all of similar construction, the interior construction being shown in absorber B which is shown in section.

, Referring to the a paratus shown in the drawings, each absorber comprises an inner receptacle 1, which may for example have an inside diameter of about 2 and a length of about 12', enclosed within another receptacle 2 in the nature of a jacket. Retaining screens 3 and 4, are arranged at the ends of the Inner receptacle, and the silica gel is sup orted between them. In an absorber of t e dimensions just mentioned, about 1500 pounds of silica gel may be used. A. connection 5 and a connection 6 communicate with the upper and lower end, respectively, of the inner receptacle. Connections 7, 8, 9 and 10 communicate with the space within the jacket about the inner receptacle. The

Ventire absorber may with advantage be thermallyinsulated or lagged. As it passes through the lower part of the outer recep tacle 2, the connectlon 6 is arranged to provide a somewhat extended heat transferring surfacevat this point. A connection 11 is arranged for supplying the gas mixture containing chlorine to the series of absorbers, connections 12 and 13, respectively, are arranged for withdrawing' concentrated chlorine and stripped residual gas from the absorbers, and connections 14 and 15 are arranged for circulating cooling brine through the absorbers. The connection 11 may communicate directly with the blow-olf for residual gas from a compressor plant for the liqluefaction of chlorine. The concentrated ch orine connection 12 is advantageously arranged to communicate with a vacuum pump and a receiver for the chlorine through suitable drying apparatus, for example aparatus for drying the chlorine by treating 1t with sulpburic acid.

As the valves are arranged in the same way for each absorber,they will be speciiicallydescribed in connection with but one of the absorbers, and it will be understood that the valve on any one of the absorbers can be desi ated bythe reference numeral for that va ve as speciically described with the reference letter for the particular absorber appended. Valves 25 are arranged to permit any one of the absorbers to be con- `ad acent absor er thro animos nected to the supply line for the gas mixture containing chlorine. Valves 16 are arranged to permit the as mixture escapin from an h connection to be le through the next a rber. Valves 17 are arranged to permit any one of the absorbers to be connected to the line for withabsorber D and o drawal of concentrated chlorine. Valves 18 are arranged to permit any one of the absorbers to 4be connected to the line for discharge of stripped residual gases. Valves 19 are arranged to ermit cool brine to be su plied to the jan ets about' any of the a f sorbers. Valves 20 are arranged to permit brine to be assed' from the jacket of one absorber eiter to the brine return line throu h valves 2,1 or to the up er end of the a jacent absorber throu h va ves 22, or to the lower end of the 'acent absorber through valves 23 and 24. rine may also be passed from the lower end of one absorber tothe upper end of the adjacent absorber through valves 23 and 22.

From the `foregoing it will be ap arent that the absorbers are arranged to operated in series and that each absorber can be progressively moved through theseries by properly7 adjusting the several valves. In carrying out the invention, it is advantageous to pass the gas mixture containing chlorine to be absorbed throu li three of theabsorbers in series while a fourth, theabsorber last handling the most concentrated gas mixture, is connected to the vacuum pump or otherwise being operated for the removal of adsorbed chlorine. For example, b opening valve 25 and closing valves 16, 1l' and 18 on absorber A and by opening valves 16 and closing valves 25 and 17 on absorbers B and C and by closing valve 18 on absorber B and opening valve 18 on absorber C the gas mixture containing chlorine is passed successively through absorbers A," B and C from the su plygline 11 to the residual gas discharge Ame 13; while at the same time by closing valves 25, 16 and 18 on nin valve 17 on this absorber, the adsor d c lorine is withdrawn from absorber D through the concentrated chlorine line 12.' When the absorber D is discharged so far as practicable and the absorber A fully char .valve 17 for absorber D is closed an valves 16 for absorber D and 18 for absorber D are opened, valve 18 for absorber C is closed, valve 16 forabsorber B is closed, valve 25 for absorber A is closed and valve 25 for absorber B is opened and valve '17 for absorber A is o ned so that the gas mixture containing ch orine is then passed successively through absorbers B, C and D while the absorber A is being discharged. When the absorber A is discharged and the absorber B fully charged, the operation is repeated in the same manner so that the gas mixture is passed successively `to the series. As it is common in through absorbers C, D and A while the absorber B is being discharged, and so on.

The cooling brine may be circulated through the jackets of all of the absorbers in parallel, or it may be circulated through them in series. One way of circulating tie brine through the absorbers in series is to circulate it first through the absorber through which the most concentrated chlorine-containing gas mixture is passing, then through the absorbers throughwhich the gas mixture next passes in generally concurrent flow and finally through the absorber which is being discharged. The brine can also be circulated through the absorbers through which the chlorine-containing gas mixture is passing in nerally counter-concurrent flow an fina ly through the absorber which is being discharged.

In one way of carrying out the process of the invention in the apparatus illustrated, snilicient artificial coolin is used so that the initial temperature ofthe silica gel as the chlorine-containin as mixture is first passed through it is a out 0 C. and the adsorption is carried out under a pressure of about 12 atmos heres absolute while the silica gel is disc arged under a ressure of about 1 atmosphere absolute. llhder these conditions, about 16 pounds of chlorine per pound of silica gel can be recovered per cycle from a lgas mixture containing about 50% by volume of chlorine in admixture with air and hydrogen. An apparatus containing about 1500 pounds of silica el per absorber operated on this basis with the period of the cycle about one hour would thus have an hourly capacity upwards of 350 pounds of chlorine.

In another way of carrying out the process of the invention, sulicient artificial cooling is used so that the initial temperature of the silica gel as the chlorine-containing gas mixture is irst passed through it is about 30 C. and the adsorption is carried out under a pressure of about 3 atmospheres absolute w ile the silica gel is discharged under a pressure of about 1/6 atmosphere absolute, that is about 2.45 unds per square inch absolute pressure. nder these conditions, aboutl .15 pounds of chlorine per pound of silica gel can be recovered per cyclejrom a gas mixture containing air and hydrogen with about 50% by volume of chlorine. An ap aratus containing about 1500 pounds of s1 ica gel per absorber operated on this basis with the period of the cycle about one hour would thus have an hourly capacity upwards of 200 pounds of chlorine. This hourly capacity can be increased by decreasing the peri of the cycle somewhat, in which event itimay be desirable to add one or more additional absorbers ractical operations to discharge the blow-o gases taining ch temperature range o from a com ressor plant for the liquefaction of chlorine at ressures approximating three atmospheres xisolute, this latter type of operation has several special advantages for use in conjunction with such operations. An additional compressor for the chlorinecontainin gas mixture becomes unnecessary as the ow-oi gases are under suflicient pressure to be supplied directl 'to the absorbers. High pressures whic are sometimes dangerous in handling mixtures conorine, air and hydrogen are also avoided.

In the foregoing examples it will be unl vderstood that the tem rature of the silica gel increases during t e adsorption art of the cycle and that it is not essentia to attempt to maintain it at the initial temperature during ithe entire operation. In the last described operation, for example, the temperature of the silica gel ma rise to as much as 6 C. or more. Li ewise it will-be understood that the preponderance of the cooling of the gel is ellected by vaporization of the adsorbed chlorine during the discharge part of the c cle, and that artificial cooling is ein lo edy to maintain the t e operation within the desired upper limit. Artificial cooling is not always essential although it is usuall advantageous, for example the pressure di erential used may be wide enough a good recover cooling althouglx artificial cooling would increase the recovery. The initial temperature of the silica gel may be.as high as 10 C. or higher, but it is advantageous to keep it below this value. The pressures employed durin adsorption ma be higher than those speci cally mentione and the ressures used 'during discharge of the adsor d chlorine from the silica gel may be lower than those specifically mentioned, pressures as low as 1/ pound per square inch absolute pressure or lower being useful in carrying out the invention.

This invention relates particularly to the utilization of silica gel 1n the recovery' of chlorine from gas mixtures containing the chlorine in high concentration, say upwards of about 20% by volume, and it 1s particularly in connection with the treatment of such gas mixtures containi a high proportion of chlorine thatman o the advantages of the invention are rea ized. In some as pects, however, the invention is of more general appliciition and has advantages of more generalapplication; In referring herein to ordinary atmospheric temperatures, reference smade to...temperatures in the neighborhood of 10 to 20 C.

We claim:

1. An improved method of recovering chlorine from mixtures containing the same by adsorption on silica gel which comto lhgiveV per cycle without art cial chlorine from gas mixtures containing thc same by adsorption on silica gel which comprises subjecting the chlorine-containing gas mixture to treatment with silica gel at an initial temperature not higher than about 0 vC. and thereafter separating adsorbed chlorine from the silica gel by maintaining the silica el under a lower pressure than that prevai ing during the adsorption treatment. y

4. An improved `method of recovering chlorine from gas mixtures containing not less than about 20% of chlorine bv volume which comprises subjecting the chlorine-containing gas mixture to treatment with' silica gel and thereafter separating adsorbed chlorine from the silica gel by maintaining the silica l under a lower pressure than that prevai ing during the adsorption treatment.

5. An improved method of recovering chlorine from gas mixtures containing not less than about 20% of chlorine by volume which comprises subjecting the chlorinecontaining mixture to treatment with silica gel an thereafter separating adsorbed chlorine from the silica gel by `maintaining the silica l under a lower pressure than that prevai ing during the adsorption treatment and artificially cooling the silica gel dur' the operation.

tmn improved method of recovering chlorine from gas mixtures containing not less than about 20% lof chlorine by volume which comprises subjecting the chlorine-containing gas mixture to treatment with silica l under superatmoslpheric pressure and t ereafter subjecting t sorbed chlorine to subatmospheric ressure to liberate adsorbed chlorine there rom.

7. An. improved method of recovering chlorine from gas mixtures containin not less than about 20% of chlorine by vo ume which comprises subjecting the chlorine-containing gas mixture to treatment with silica gel at an initial temperature not higher than about 0 C. and thereafter separating adsorbed chlorine from the silica gel by maintainingl the silica gel under a lower pressure than t at prevailing during the adsorption treatment.

8. An improved method of recovering chlorine from gas mixtures containing about 50% of chlorine by volume which comprises e silica gel and adno1-:3ans

subjecting the chlorine-containing gas mixture to treatment with silica gel and thereafter segarating adsorbed chlorine from the silica ge .by malntaining the silica gel under a lower pressure than that prevailing during the adsorption treatment.

9. An improved method of recovering chlorine from gas mixtures containing about 50% of chlorine b volume which comprises 10 subjecting the ch crine-containing gas mix.

ture to treatment with silica gelunder su ratmospherlc pressure and thereafter sub1ectmathe silica gel and adsorbed chlorine to su heric pressure to liberate adsorbed chlorine m the silica el.

testimony whereof ax my signature.

JESSE A, GUYER.

subjecting the chlorine-containing gas mixture to treatment with silica gel and thereafter separating adsorbed chlorine from the silica ge by maintaining the silica gel under 5 a lower pressure than that' prevailing during the adsorption treatment.

9. An improved method of recovering chlorine from gas mixtures containing about 50% of chlorine b volume which comprises 10 subjecting the ch crine-containing gas mix-l JESSE A. GUYER. In testimony whereof I allix my signature.

MAURICE C. TAYLOR.

CERTIFICATE 0F CCRRECTION.

Patent No. l, 617, 305.

Granted February 8, 1927, to

lt is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 95. before. the numeral "16". insert a decimal point making it read ".l6"; and that the said Letters Patent should be read with this correction therein that the same may conformv to the record of the case in the Patent Office.

Signed andsealed this 10th day of May. A. D. 1927.

-Seal.

M. I. Moore, Acting Commissioner of Patente.

CERTIFICATE GF CORRECTION.

Potent No. 1,617,305. Granted February 8, [927, to

JESSE A. GUYER ET'AL.

It is hereby certified that error appears in the printed specification of the 'above numbered potent requiring correction as follows: Page 3, line 95, before the numeral "16" insert a decimal point making it read 16"; Ind that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed und sealed this 10th day of May. A. D. 1927.

M. J. Moore.

SeaL Acting Commissioner of Patents. 

